Aromatic carbonate resins are well known thermoplatic materials which due to their many advantageous properties find use as thermoplastic engineering materials. The aromatic carbonate resins exhibit, for example, excellent properties of toughness, flexibility, and thermal stability, particularly thermal dimensional stability. The aromatic carbonate resins and methods for their preparation are disclosed, inter alia, in U.S. Pat. Nos. 2,964,974, 2,999,835, 3,169,121, 3,028,365, 3,334,154, 3,275,601 and 3,915,926.
However, the impact properties, particularly impact strength, of these aromatic carbonate resins are generally not sufficiently high for certain applications. This is particularly true of their thick section, i.e., one-quarter inch and thicker, impact strength.
It is known that the impact properties of polycarbonates can be upgraded by combining the polycarbonate resins with impact modifiers. U.S. Pat. No. 4,148,842 of Yu et al. discloses blends of a polycarbonate resin and an interpolymer modifier comprising crosslinked (meth)acrylate, crosslinked styrene-acrylonitrile, and uncrosslinked styrene acrylonitrile. This impact modifier is described in U.S. Pat. No. 3,944,631 of Yu et al. as being a three-stage impact modifier produced in a three-stage polymerization procedure in which in the third stage, a crosslinked acrylate/crosslinked styrene-acrylonitrile polymeric material is used as a reaction ingredient during the polymerization of styrene and acrylonitrile without a crosslinking agent.
It has now been discovered that a two-phase material, i.e., a crosslinked acrylate/crosslinked styreneacrylonitrile, produced by a two-stage polymerization procedure, can be utilized as an effective impact modifier for thermoplastic aromatic carbonate resins such as polycarbonates and copolyester-carbonates. The use of this two-phase interpolymer comprised of a crosslinked elastomeric acrylate and a crosslinked styrene-acrylonitrile is tuus a departure from known techniques described in the prior art. For example, in the aforesaid U.S. Pat. No. 3,944,631 and 4,148,842 a three-stage polymerizations yielding a three-phase interpolymer comprised of a crosslinked acrylate/crosslinked styrene-acrylonitrile/uncrosslinked or linear stryene-acrylonitrile are advocated, rather than a two-stage polymerization yielding a two-phase interpolymer followed by a blending step, as discussed herein.
The fact that the two-phase crosslinked acrylate/crosslinked styrene-acrylonitrile interpolymer can be used effectively in aromatic carbonate resins as an impact modifier is generally surprising and unexpected. In order for a material to function as an effective impact modifier for aromatic carbonate resins it must not only improve the impact properties of the resins but must also be compatible with the aromatic carbonate resins, that is, it must not deleteriously affect the advantageous properties of the resins. Furthermore, it must be readily combinable with aromatic carbonate resins over the range of concentrations which are effective to improve the impact properties of the resins. While some materials act to improve the impact properties of aromatic carbonate resins, they do so only at the cost of deleteriously affecting some of the other advantageous properties of the resins. While other materials function as impact modifiers for aromatic carbonate resins and do not significantly deleteriously affect substantially most of the other advantageous properties of these resins, they are not readily combinable with the aromatic carbonate resins. Still other materials need to be present in relatively large concentrations in order to significantly upgrade the impact properties of aromatic carbonate resins. The area of improving the impact properties of aromatic carbonate resins by blending them with various impact modifiers is thus still an art wherein the empirical approach is still generally the rule.
Thus, the fact that the instant two-phase cross-linked interpolymers function as effective impact modifiers for aromatic carbonate resins, in that they positively upgrade the imact properties of aromatic carbonate resins at relatively low loadings, are compatible with these resins, and are readily combinable with aromatic carbonate resins, could not have been predicted and is unexpected.